Master-slave type telemanipulators are of course made up of a master arm, having a control handle accessible to an operator, and a slave arm which is generally identical or similar to the master arm and has a tool, such as gripping tongs. The slave arm is disposed inside a cell which is inaccessible to people, because of the presence of a dangerous atmosphere or dangerous products, such as radioactive products, inside the cell. The master arm and the slave arm have the same number of degrees of freedom and are connected mechanically through the wall of the cell, so that any movement of the master arm and/or its control handle initiated by the operator causes an identical or similar movement of the slave arm and/or the gripping tongs. An observation window in the compartment of the cell therefore enables the operator to perform the required handling inside the cell.
Master-slave telemanipulators are also subdivided into two main families. The first of the families contains articulated telemanipulators in which the master and slave arms are each made up of a number of articulated segments which reproduce movements comparable to those of the human arm; most frequently two segments are provided. The second of these families, which is the only one to which the present invention relates, contains telescopic telemanipulators in which each arm is made up of a number of segments telescopically mounted so as to enable the length of the arm to be modified.
More precisely, master-slave type telescopic telemanipulators according to the invention are made up of a telescopic master arm and a telescopic slave arm, such arms being articulated to a traversing block around two normally parallel shoulder pivots which are orthogonal to the axis of the block, the traversing block traversing the compartment of the cell and being mounted to rotate around its own axis. The end of each of the arms therefore has three degrees of positioning freedom, to which are added the degrees of freedom of the control handle and of the tongs, which are mentioned here merely as a reminder, since they do not affect the equilibration of the arms. Conventionally in the following description the degrees of freedom bound up with the positioning of each of the arms will be referred to as follows:
X: rotation of the arms around the axis of the traversing block; PA1 Y: rotation of the arms around their shoulder pivots; PA1 Z: variation in the length of the arms.
To extend the range of telemanipulators and make access to certain zones of the cell easier, as a rule such telemanipulators have means enabling the slave arm to be offset in relation to the master arm in accordance with one or more of the degrees of freedom X, Y and Z, independently of any movement of the master arm.
For various reasons, more particularly to do with the space occupied by the equilibrating counterweights and the need to estimate the number of mechanisms disposed inside the cell to that strictly necessary, having regard to handling difficulties inside the cell, the means for equilibrating the slave arm are disposed, like those of the master arm, outside the cell. However, the equilibration of the slave arm is of course made particularly complex by the possibility of its becoming offset in relation to the master arm in accordance with one or more of the degrees of freedom X, Y and Z, combined with the need to dispose all the equilibrating means outside the cell.
Up to date two master-slave telescopic telemanipulators are known in which the slave arm is equilibrated by two practically opposite techniques.
Thus, in the first known telemanipulator of this kind, a link bearing a first counterweight is retained always parallel with the slave arm when there is no offsetting in X between the master and slave arms. Moreover, the counterweight which ensures the equilibration of the master arm when its length Z varies, at the same time equilibrates the slave arm correspondingly. However, the slave arm is no longer correctly equilibrated by the first counterweight when there is an offsetting in X or Z between the two arms. Moreover, the equilibration in Z of the slave arm by the second counterweight is unsatisfactory, since the corresponding mass becomes parasitic when there is an offsetting in X or Y of the slave arm, all the more so since the latter thus approaches the horizontal. Such defects in equilibration are very troublesome to the operator and make the operation of that telemanipulator particularly difficult.
The second master-slave type telescopic telemanipulator hitherto known in contrast ensures the perfect equilibration of the slave arm in all its positions, whatever offsettings may be introduced between the slave and master arms. However, this result is based on a very complex mechanism which makes the telemanipulator relatively unreliable and above all very substantially increases its price. Moreover, the telemanipulator comprises a counterweight mounted directly on the slave arm in order to compensate its movement in Z; this is undesirable for the reasons of accessibility already stated, and also because this type of mobile counterweight directly mounted on the arm correspondingly increases the mass of the counterweight, which moreover serves to equilibrate the arm assembly.
It is an object of the invention to provide a master-slave type telescopic telemanipulator which equilibrates the slave arm substantially more satisfactorily than the first-mentioned prior art type of telemanipulator and which costs less and is substantially more reliable than the second-mentioned prior art type of telemanipulator.